Current manned military submarines usually have an electric motor arranged in the submarine as their propulsion drive, which via a propeller shaft drives a propeller arranged in a longitudinal direction outside the hull of the boat as an extension of the stern. To this end the propeller shaft must penetrate the hull of the submarine in the submarine's stern. The sealing at the point of penetration is provided in such cases by a shaft sealing ring. With some types of submarine two propeller shafts can also be fed in the stern through the boat hull and via a propeller shaft (one propeller each on the starboard side and on the port side) drive two propellers arranged outside the hull of the boat in a longitudinal direction as an extension of the stern.